This renewal application reflects a new and important step in the pursuit of the mechanisms by which the RAS contributes to the evolution of cardiovascular disease through our characterization of a homolog of angiotensin converting enzyme (ACE), ACE2, which negatively regulates the actions of the system by metabolizing Ang II into the vasodilator and anti-proliferative heptapeptide Ang-(1-7). Preliminary characterization of ACE2, to which this program contributed directly, showed that the ACE2 gene maps to defined quantitative trait loci on the X chromosome in three different rat models of hypertension, while in mice, targeted disruption of ACE2 is associated with high plasma levels of Ang II and impaired cardiac contractility. These new findings bolster the underlying hypothesis of this program which first documented a role of Ang-(1-7) in opposing the actions of Ang II. Analysis of the interplay among ACE, ACE2, and Ang-(1-7) in the regulation of heart function, renal excretory function, central regulation of baroreflexes, and the utero-placental circulation in pregnant rats suggest that Ang-(1-7) produced by ACE2 counter-balances the activity of Ang II. Characterization of the actions of ACE2 and Ang-(1-7) and the identification of mas and the AT1b receptor as putative Ang-(1-7) binding sites is now the focus of the proposed research of this renewal application through the aggregate effort of five proposed projects and four Core Resource Units. Project 1 will determine the role of ACE and Ang-(1-7) in the development of hypertension-mediated cardiac hypertrophy. Dr. Tallant's project will examine the role of ACE2 in Ang-(1-7)-mediated growth regulation of cardiac myocytes and fibroblasts. Dr. Chappell's project will investigate the role of ACE and ACE2 in regulating the expression of both Ang II and Ang-(1-7) in the kidney. Dr. Diz's project will analyze the effects of Ang-(1-7) in the central control of baroreceptor function in aging and the interaction of this peptide with brain mas and AT1b receptors. Dr. Brosnihan's project will assess the role of enhanced ACE2 expression during pregnancy and its dysregulation during pregnancy-induced hypertension. Four Cores (Administration and Biostatics, Molecular and Cellular Biology, Biochemistry, and Animal Resource) support the integrative effort of the investigators, such that sharing of research tools and techniques allows the development of multi-faceted experimentation. The research will employ a new congenic rat model of hypertension developed in our program, rats with under-expression of brain angiotensinogen, and ACE2 and AT1b knockout mice.